1. Field of the Invention
This invention relates to electrical protection of conductors and components of a rigid electrical assembly. In particular, aspects of the invention relate to using a conductive layer to protect electrical connectors used in rigid electrical rafts to distribute electrical signals around a gas turbine engine, and to protect electrical units mounted on the rigid electrical rafts.
2. Description of the Related Art
A typical gas turbine engine has a substantial number of electrical components which serve, for example, to sense operating parameters of the engine and/or to control actuators which operate devices in the engine. Such devices may, for example, control fuel flow, variable vanes and air bleed valves. The actuators may themselves be electrically powered, although some may be pneumatically or hydraulically powered, but controlled by electrical signals.
Electrical power, and signals to and from the individual electrical components, is commonly transmitted along conductors. Conventionally, such conductors may be in the form of wires and/or cables which are assembled together in a harness. In such a conventional harness, each wire may be surrounded by an insulating sleeve, which may be braided or have a braided cover.
By way of example, FIG. 1 of the accompanying drawings shows a typical gas turbine engine including two conventional wiring harnesses 102, 104, each provided with a respective connector component 106, 108 for connection to circuitry, which may be for example accommodated within the airframe of an aircraft in which the engine is installed.
The harnesses 102, 104 are assembled from individual wires and cables which are held together over at least part of their lengths by suitable sleeving and/or braiding.
Individual wires and cables, for example those indicated at 110, emerge from the sleeving or braiding to terminate at plug or socket connector components 112 for cooperation with complementary socket or plug connector components 114 on, or connected to, the respective electrical components.
Each conventional harness 102, 104 comprises a multitude of insulated wires and cables. This makes the conventional harness itself bulky, heavy and difficult to manipulate. The conventional harnesses occupy significant space within a gas turbine engine (for example within the nacelle of a gas turbine engine), and thus may compromise the design of the aircraft, for example the size and/or weight and/or shape of the nacelle.
Conventional harnesses comprise a large number of components, including various individual wires and/or bundles of wires, supporting components (such as brackets or cables) and electrical and/or mechanical connectors. This can make the assembly process complicated (and thus susceptible to errors) and/or time consuming. Disassembly of the conventional harnesses (for example removal of the conventional harnesses from a gas turbine engine during maintenance) may also be complicated and/or time consuming. Thus, in many maintenance (or repair or overhaul) procedures on a gas turbine engine, removal and subsequent refitting of the conventional electrical harness may account for a very significant portion of the operation time and/or account for a significant proportion of the potential assembly errors.
The electrical conductors in the conventional harnesses may be susceptible to mechanical damage. For example, mechanical damage may occur during installation (for example through accidental piercing of the protective sleeves/braiding) and/or during service (for example due to vibration). In order to reduce the likelihood of damage to the conductors in a conventional harness, the protective sleeves/braiding may need to be further reinforced, adding still further weight and reducing the ease with which they can be manipulated. Similarly, the exposed electrical connectors used to connect one conductor to another conductor or conductors to electrical units may be susceptible to damage and/or may add significant weight to the engine.
The electrical conductors in the conventional harnesses may be susceptible to electromagnetic damage and/or interference. For example, the electrical conductors may interfere with each other. This may mean that electrical signals may suffer unwanted and unknown changes as they pass along the conductors. Additionally or alternatively, electrical damage and/or interference may be caused by electrical surges, for example due to lightening strikes. In order to try to avoid/minimize this potential damage/interference, individual wires and/or bundles in the conventional electrical harness may be provided with sleeving and/or braiding. This adds significant weight to the harness, and thus to the engine. The weight gain may be particularly significant where many separate sleeves and/or braids need to be applied to individual wires and/or only small collections of wires.
Electromagnetic damage and/or interference may also occur to electrical units (such as electronic control units) mounted on a gas turbine engine, for example due to lightening strikes. Such damage could be extremely serious, and so protection is required. Conventionally, therefore, an electrical grounding path is provided from the electrical units to the rest of the engine. This may take the form of electrical connection of the casing of the electrical unit to an electrically conductive component mounted on the engine. The electrical protection of the electrical units is provided separately from the electrical protection of the electrical conductors in the conventional harness. This adds complexity (for example in terms of part count) and weight to the engine, and also adds to the assembly time.